1. Field of the Invention
The present invention is directed to a presentation device for presenting a volume dataset with a number of volume data elements as a perspective, two-dimensional image rotatable around a basic rotational axis.
2. Description of the Prior Art
Presentation devices of the above type are known which have a data memory for storing the volume dataset, a computer unit for determining the image from the volume data elements of the volume dataset, a display unit, for example a monitor, at least for the presentation of the image and at least one input means, for example a keyboard and/or a mouse control. In such known devices, respective positions in the volume and a data value are allocated to each volume data element. The computer unit has at least one boundary surface prescribed to it via the input means on the basis of which the volume dataset is divided into a selection dataset and a remaining dataset that is complementary to the volume dataset. Only volume data elements that are contained in the selection dataset are utilized for the determination of the two-dimensional image.
Such presentation devices are employed in medical fields for the presentation of tomograms or other three-dimensional reconstructions of patient images, for example in X-ray angiography. An especially relevant region of the volume dataset can be selected in a simple way by suitably prescribing the boundary surface, and further boundary surfaces as well, if needed. By rotation of the image, the relevant region can be observed from different viewing angles.
In such known devices, the basic rotational axis usually proceeds through the center of gravity of the volume dataset, i.e. through the middle of the volume defined by the volume dataset. This is disadvantageous for some presentations. This disadvantage is particularly apparent when only a part of the volume dataset is displayed on the display unit, and the rotational axis lies outside the displayed volume region.
U.S. Pat. No. 5,891,030 discloses a device that reproduces tubular structures of a human body, for example the gastrointestinal tract, with the assistance of a CT scanner with a work station. The center line of the large intestine is thereby identified. The work station compiles CT data such that axial tomograms, transluminal cross-sectional images and intraluminal volume rendering images are shown.
U.S. Pat. No. 5,463,722 discloses an apparatus for the automatic alignment of manipulated objects in the two-dimensional and three-dimensional graphics space.
U.S. Pat. No. 5,644,689 discloses a method for a three-dimensional presentation from an arbitrary point of view that employs compressed voxel data that were produced by a direct search for voxel data representing an image of a subject.
An object of the present invention is to provide a presentation device that does not exhibit the aforementioned disadvantages of the known devices.
This object is achieved in a presentation device wherein that the basic rotational axis is selectable dependent on the positions of the volume data elements of the selection dataset, and in particular, is automatically determined by the computer unit dependent on the positions of the volume data elements of the selection dataset.
The invention allows namely, the basic rotational axis to be placed at least in the proximity of a selection volume defined by the selection dataset. The basic rotational axis preferably touches the selection volume, or intersects it.
The presentation is especially stable when the selection volume has a selection volume center of gravity and the basic rotational axis proceeds through the selection volume center of gravity.
The presentation is especially flexible in an embodiment wherein the image can be rotated around at least one auxiliary rotational axis, the auxiliary rotational axis intersecting the basic rotational axis, and wherein the auxiliary rotational axis is also selectable dependent on the positions of the volume data elements of the selection dataset. In particular, this auxiliary rotational axis can be automatically defined by the computer unit dependent on the positions of the volume data elements of the selection dataset. The above statements for the basic rotational axis apply by analogy to the positioning of the auxiliary rotational axis.
The advantages of the invention are particularly apparent when the image is scalable and/or displaceable.
Fundamentally, the boundary surface can also be an arbitrary, even a curved surface. Generally, however, it is a plane.
Fundamentally, the planes can be arbitrarily oriented in space. When the position of the volume data elements is defined by three coordinates of a Cartesian coordinate system, however, these planes proceed perpendicularly to one of the coordinate axes.
When the boundary surfaces can be displayed by the display unit together with the displayed image, the region that has been selected can be immediately seen.
The presentation is especially flexible when the boundary surface is interactively displaceable.